How the Size of the Ureteric Access Sheath Affects Kidney Irrigation Flow

When performing ureteroscopy, the size of the ureteric access sheath (UAS) can dramatically influence irrigation flow and intrarenal pressure.

To demonstrate this, we set up a simple model using three common sheath sizes:

• Fr 10/12 (smallest)

• Fr 11/13 (medium)

• Fr 12/14 (largest)

Inside each sheath, we placed an Fr 8.6 ureteroscope. The irrigation bag was set to 40 cm H₂O, the upper safe limit for driving pressure.

This model demonstrates the influence of the ureteric access sheath (UAS) size on irrigation flow relative to the ureteroscope size, and ultimately on intrarenal pressure.

What We Observed

When running the irrigation, the differences were clear: Fr 12/14 (largest sheath) produces a continuous flow. Fr 11/13 (intermediate sheath) shows a moderate flow. Fr 10/12 (smallest sheath) drips very slowly, with hardly any fluid exiting.

Increasing the height of the irrigation bag (and thus pressure) improved flow for the medium and large sheaths but made almost no difference for the smallest sheath (Fr 10/12). The flow was essentially “fixed,” demonstrating that small sheaths severely restrict fluid exit regardless of pressure.

Why This Matters

• Restricted flow leads to pressure buildup inside the kidney, which can be risky during procedures.

• Choosing the right sheath size should depend on the ureteroscope being used, not the patient’s size.

• Correct sheath selection ensures:

  • Safe intrarenal pressure

  • Efficient irrigation

  • Reduced procedure complications